The possibility of developing optoelectronic emitter and detector device structures in a wide spectral range—from the infrared (IR) to ultraviolet (UV)—as well as high-frequency transistors operating at high powers and temperatures, has generated significant interest in group III-nitride compounds (e.g., indium nitride, gallium nitride, and aluminum nitride). These materials are mainly produced as epitaxially deposited films by metalorganic vapor phase epitaxy (MOVPE), which is sometimes referred to as metalorganic chemical vapor deposition (MOCVD or OMCVD), and molecular beam epitaxy (MBE). When halide compounds are utilized the process may also be referred to as halide vapor transport epitaxy (HVTE) or halide vapor phase epitaxy (HYPE). In MOCVD, a reactive gas flow is transported through a reaction zone (also denoted as a deposition zone), undergoes gas-phase decomposition reactions, reactive products diffuse towards the substrate surface, and surface reactions occur in the deposition zone on the substrate. The reactive precursor fragments become physi-sorbed and/or chemi-sorbed at the growth surface, diffuse, and nucleate at reaction sites, resulting in film growth.
However, indium-rich group III-nitrides and many other compounds, including oxygen-containing alloys, are highly susceptible to thermal decomposition at their optimum kinetic growth temperatures. Indium nitride (InN) is one of the most difficult group III-nitride semiconductor alloys to synthesize, since the equilibrium vapor pressure of nitrogen over InN is much higher compared to nitrogen over aluminum nitride (AlN) and nitrogen over gallium nitride (GaN), which makes it difficult to integrate InN into GaN- or MN-based device structures. FIG. 1 shows the thermal decomposition pressures for the binary compounds AlN, GaN, and InN as a function of temperature.
The integration of higher concentrations of indium into group III-nitride alloys such as Inl-xGaxN is a major challenge using low-pressure deposition techniques such as MBE and MOCVD due to thermodynamic stabilization limitations. Off-equilibrium approaches such as plasma-assisted MBE have been applied to transiently stabilize indium-rich group III-nitride alloys, but these techniques have not solved the fundamental problem of making thermodynamically stable products. For instance, in order to integrate indium-rich In1-xGaxN layers into a wide band gap group III-nitride heterostructure, indium-rich In1-xGaxN layers have to be stabilized at typical MOCVD conditions using temperatures between 800° C. and 1100° C. However, in common low-pressure processes, InN growth temperatures at or below 650° C. are required in order to stabilize the alloy. As the indium-content in In1-xGaxN increases, the growth temperature has to be increased and the group III-V precursor ratio adjusted. Thus, the required adjustment of the growth temperature for various indium fractions limits the quality of the In1-xGaxN layers and/or their integration within the same device structure. Presently, only materials with small amounts of indium (x≧0.75) have been made with considerable quality, while at higher indium mole fractions there seems to be a miscibility gap. F. K. Yam and Z. Hassan, InGaN: An overview of the growth kinetics, physical properties and emission mechanisms, Superlattices and Microstructures 43(1), pp. 1-23 (2008). Accordingly, there is a need for new systems and methods for providing thermodynamically stable alloys incorporating heterolayers with different partial pressures and thermal stabilities such that useful semiconductor materials may be obtained.